# C++ Internal linkage

**[Internal linkage](https://en.cppreference.com/w/cpp/language/linkage)** means a symbol (function, variable, or type) is visible only within its translation unit and not to other .cpp files. Declaring with `static` or in an anonymous namespace gives internal linkage. This prevents linker conflicts and allows using the same name in different translation units.

Use `static` or anonymous namespaces for helper functions and variables that should not be visible to other translation units.

## Example

This example shows internal linkage preventing naming conflicts across files.

```cpp
// compile: g++ -o internal internal.cpp
// run: ./internal
// description: internal linkage limits visibility to one translation unit

#include <iostream>

// Method 1: static (internal linkage)
static void helperA() { std::cout << "Helper A\n"; }

// Method 2: anonymous namespace (preferred, internal linkage)
namespace {
    void helperB() { std::cout << "Helper B\n"; }
    int internal_counter = 0;
}

// External linkage (visible to other translation units)
void public_func() { std::cout << "Public\n"; }

int main() {
    helperA();
    helperB();
    public_func();
    
    return 0;
}
```